1. Field of the Invention
The present invention relates to an interference measurement and evaluation system, more particularly relates to an interference measurement and evaluation system for estimating a receiving line quality characteristic due to nonlinear interference, reception thermal noise power, leakage power from an adjacent channel, etc. In a communication or broadcasting system using radio waves or optical communications.
2. Description of the Related Art
Wireless communication systems mainly suffer from mutual interference not only between terrestrial mobile wireless systems and terrestrial fixed wireless systems, but also between commercial wireless systems for space and mobile satellite communication systems. These mutual interferences include linear interference due to leakage power from adjacent or next-to-adjacent areas or linear interference due to frequency sharing and nonlinear interference where intermodulation distortion occurs due to high level interference power. In areas where the service area are broad and many systems coexist, the study of nonlinear interference has been becoming important. These are also present in optical communications and broadcasting.
For example, in areas with a coexistence of wireless systems such as conventional mobile wireless communication systems together or a mobile wireless communication system, terrestrial fixed microwave communication system, and mobile satellite communication system, the line quality has been evaluated by the leakage power of the linear parts of interference waves, filtering at the receiving side, the modulation/demodulation scheme, etc., but the nonlinear interference has not been sufficiently evaluated.
Further, while the performance relating to nonlinear interference in a receiver by themselves and individual specifications inside apparatuses of interfered wireless systems have been known, there has never been a means for estimating the above specifications as overall receiver performance in a transmitter and a receiver system.
Nonlinear distortion has been analytically verified in the past. In this, using mathematical algorithms and introducing the third-order intercept point input level (IIP3) technique, the spread of an intermodulation product (IM) spectrum by a modulated wave, the occurrence of an interference wave due to IM, and the sensitivity suppression have been studied (for example, see “Study of Nonlinear Interference Theory Relating to Wide Band Mobile Wireless System and Narrow Band Mobile Wireless System”, Journal of the EIAJ, EIAJ, RCS2002-140, Aug. 22, 2002, and “Intercept Point and Undesired Responses”, JEEE Transaction on Vehicular Technology, vol. VT32, no. 1, February 1983).
Summarizing the problems to be solved by the invention, as explained above, in the past, sufficient nonlinear distortion was not taken against nonlinear interference, so there was the problem that it was not possible to analyze the cases of occurrence of nonlinear distortion due to nonlinearity of a receiver and power of the interfering wave, the frequency interval between the desired wave and interference wave, etc., so as to reduce the frequency of occurrence and deterioration of quality in the service area.